The specific aim of the proposed research is to design, analyze, and construct physical models that have absorption properties for microwave, UHF, and short wave electromagnetic energy and heat clearance properties similar to those of living tissue. The intended use of these models is in the study of heating properties of tissues for use in the design and testing of clinical hyperthermia applicators. The proposed models will allow highly sophisticated analysis of devices intended for clinical use, which will facilitate the design process and minimize the use of in vivo animal experiments. The models will be constructed from gels and microemulsions whose water contents are comparable to those of soft tissues with high water content (e.g., muscle) or low water contents (e.g., bone and fat). It is shown in the proposal that suitable materials can be prepared, with bulk electrical characteristics and material thermal properties that approximate those of tissue. The convective cooling (which in living tissue arises from blood perfusion) will be modelled as heat removal by water passing through a capillary bundle that is embedded in the matrix. By proper choice of total flow rates, diameters, and number density of capillary tubes, the overall thermal properties of the model will be made to closely approximate those of a living tissue. The heat clearance properties of the model will be established by means of (a) computer finite element calculations of the transient and steady state thermal response to a heat input assuming convective boundary conditions, and (b) experimentally in models using a heated probe and measurement of the steady state and transient thermal response throughout the model. These measurements will be related to the convective and conductive heat transfer properties of the system. Finally, the heating behavior of the model will be studied, using practical hyperthermia applicator systems and thermistor probe or thermographic measurement techniques.